Avoid a scrape_region_constraints and instead register the region constraints directly

Author: oli-obk

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -248,13 +248,50 @@ impl<'tcx> InferCtxt<'tcx> {
     where
         R: Debug + TypeFoldable<TyCtxt<'tcx>>,
     {
-        let InferOk { value: result_args, mut obligations } = self
-            .query_response_instantiation_guess(
-                cause,
-                param_env,
-                original_values,
-                query_response,
-            )?;
+        let result_args =
+            self.query_response_instantiation_guess(cause, original_values, query_response);
+
+        let mut obligations = vec![];
+
+        // Carry all newly resolved opaque types to the caller's scope
+        for &(opaque_type_key, hidden_ty) in &query_response.value.opaque_types {
+            let opaque_type_key = instantiate_value(self.tcx, &result_args, opaque_type_key);
+            let hidden_ty = instantiate_value(self.tcx, &result_args, hidden_ty);
+            debug!(?opaque_type_key, ?hidden_ty, "constrain opaque type");
+            // We can't use equate here, because the hidden type may have been an inference
+            // variable that got constrained to the opaque type itself. In that case we want to ensure
+            // any lifetime differences get recorded in `ouput_query_region_constraints` instead of
+            // being registered in the `InferCtxt`.
+            match hidden_ty.kind() {
+                ty::Alias(ty::Opaque, alias_ty)
+                    if alias_ty.def_id == opaque_type_key.def_id.into() =>
+                {
+                    assert_eq!(alias_ty.args.len(), opaque_type_key.args.len());
+                    for (key_arg, hidden_arg) in
+                        opaque_type_key.args.iter().zip(alias_ty.args.iter())
+                    {
+                        self.equate_generic_arg(
+                            key_arg,
+                            hidden_arg,
+                            output_query_region_constraints,
+                            ConstraintCategory::OpaqueType,
+                            &mut obligations,
+                            cause,
+                            param_env,
+                        )?;
+                    }
+                }
+                _ => {
+                    self.insert_hidden_type(
+                        opaque_type_key,
+                        cause,
+                        param_env,
+                        hidden_ty,
+                        &mut obligations,
+                    )?;
+                }
+            }
+        }
 
         // Compute `QueryOutlivesConstraint` values that unify each of
         // the original values `v_o` that was canonicalized into a
@@ -381,25 +418,47 @@ impl<'tcx> InferCtxt<'tcx> {
             original_values, query_response,
         );
 
-        let mut value = self.query_response_instantiation_guess(
-            cause,
-            param_env,
-            original_values,
-            query_response,
-        )?;
+        let result_args =
+            self.query_response_instantiation_guess(cause, original_values, query_response);
 
-        value.obligations.extend(
+        let mut obligations = vec![];
+
+        // Carry all newly resolved opaque types to the caller's scope
+        for &(opaque_type_key, hidden_ty) in &query_response.value.opaque_types {
+            let opaque_type_key = instantiate_value(self.tcx, &result_args, opaque_type_key);
+            let hidden_ty = instantiate_value(self.tcx, &result_args, hidden_ty);
+            debug!(?opaque_type_key, ?hidden_ty, "constrain opaque type");
+            // We use equate here instead of, for example, just registering the
+            // opaque type's hidden value directly, because the hidden type may have been an inference
+            // variable that got constrained to the opaque type itself. In that case we want to equate
+            // the generic args of the opaque with the generic params of its hidden type version.
+            obligations.extend(
+                self.at(cause, param_env)
+                    .eq(
+                        DefineOpaqueTypes::Yes,
+                        Ty::new_opaque(
+                            self.tcx,
+                            opaque_type_key.def_id.to_def_id(),
+                            opaque_type_key.args,
+                        ),
+                        hidden_ty,
+                    )?
+                    .obligations,
+            );
+        }
+
+        obligations.extend(
             self.unify_query_response_instantiation_guess(
                 cause,
                 param_env,
                 original_values,
-                &value.value,
+                &result_args,
                 query_response,
             )?
             .into_obligations(),
         );
 
-        Ok(value)
+        Ok(InferOk { value: result_args, obligations })
     }
 
     /// Given the original values and the (canonicalized) result from
@@ -411,14 +470,13 @@ impl<'tcx> InferCtxt<'tcx> {
     /// will instantiate fresh inference variables for each canonical
     /// variable instead. Therefore, the result of this method must be
     /// properly unified
-    #[instrument(level = "debug", skip(self, param_env))]
+    #[instrument(level = "debug", skip(self))]
     fn query_response_instantiation_guess<R>(
         &self,
         cause: &ObligationCause<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
         original_values: &OriginalQueryValues<'tcx>,
         query_response: &Canonical<'tcx, QueryResponse<'tcx, R>>,
-    ) -> InferResult<'tcx, CanonicalVarValues<'tcx>>
+    ) -> CanonicalVarValues<'tcx>
     where
         R: Debug + TypeFoldable<TyCtxt<'tcx>>,
     {
@@ -491,7 +549,7 @@ impl<'tcx> InferCtxt<'tcx> {
         // Create result arguments: if we found a value for a
         // given variable in the loop above, use that. Otherwise, use
         // a fresh inference variable.
-        let result_args = CanonicalVarValues {
+        CanonicalVarValues {
             var_values: self.tcx.mk_args_from_iter(
                 query_response.variables.iter().enumerate().map(|(index, info)| {
                     if info.universe() != ty::UniverseIndex::ROOT {
@@ -516,31 +574,7 @@ impl<'tcx> InferCtxt<'tcx> {
                     }
                 }),
             ),
-        };
-
-        let mut obligations = vec![];
-
-        // Carry all newly resolved opaque types to the caller's scope
-        for &(a, b) in &query_response.value.opaque_types {
-            let a = instantiate_value(self.tcx, &result_args, a);
-            let b = instantiate_value(self.tcx, &result_args, b);
-            debug!(?a, ?b, "constrain opaque type");
-            // We use equate here instead of, for example, just registering the
-            // opaque type's hidden value directly, because the hidden type may have been an inference
-            // variable that got constrained to the opaque type itself. In that case we want to equate
-            // the generic args of the opaque with the generic params of its hidden type version.
-            obligations.extend(
-                self.at(cause, param_env)
-                    .eq(
-                        DefineOpaqueTypes::Yes,
-                        Ty::new_opaque(self.tcx, a.def_id.to_def_id(), a.args),
-                        b,
-                    )?
-                    .obligations,
-            );
         }
-
-        Ok(InferOk { value: result_args, obligations })
     }
 
     /// Given a "guess" at the values for the canonical variables in

compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs

@@ -159,70 +159,53 @@ where
             .0);
         }
 
-        let mut error_info = None;
         let mut region_constraints = QueryRegionConstraints::default();
-
-        // HACK(type_alias_impl_trait): When moving an opaque type to hidden type mapping from the query to the current inferctxt,
-        // we sometimes end up with `Opaque<'a> = Opaque<'b>` instead of an actual hidden type. In that case we don't register a
-        // hidden type but just equate the lifetimes. Thus we need to scrape the region constraints even though we're also manually
-        // collecting region constraints via `region_constraints`.
-        let (mut output, _) = scrape_region_constraints(
-            infcx,
-            |_ocx| {
-                let (output, ei, mut obligations, _) =
-                    Q::fully_perform_into(self, infcx, &mut region_constraints, span)?;
-                error_info = ei;
-
-                // Typically, instantiating NLL query results does not
-                // create obligations. However, in some cases there
-                // are unresolved type variables, and unify them *can*
-                // create obligations. In that case, we have to go
-                // fulfill them. We do this via a (recursive) query.
-                while !obligations.is_empty() {
-                    trace!("{:#?}", obligations);
-                    let mut progress = false;
-                    for obligation in std::mem::take(&mut obligations) {
-                        let obligation = infcx.resolve_vars_if_possible(obligation);
-                        match ProvePredicate::fully_perform_into(
-                            obligation.param_env.and(ProvePredicate::new(obligation.predicate)),
-                            infcx,
-                            &mut region_constraints,
-                            span,
-                        ) {
-                            Ok(((), _, new, certainty)) => {
-                                obligations.extend(new);
-                                progress = true;
-                                if let Certainty::Ambiguous = certainty {
-                                    obligations.push(obligation);
-                                }
-                            }
-                            Err(_) => obligations.push(obligation),
+        let (output, error_info, mut obligations, _) =
+            Q::fully_perform_into(self, infcx, &mut region_constraints, span).map_err(|_| {
+                infcx.dcx().span_delayed_bug(span, format!("error performing {self:?}"))
+            })?;
+
+        // Typically, instantiating NLL query results does not
+        // create obligations. However, in some cases there
+        // are unresolved type variables, and unify them *can*
+        // create obligations. In that case, we have to go
+        // fulfill them. We do this via a (recursive) query.
+        while !obligations.is_empty() {
+            trace!("{:#?}", obligations);
+            let mut progress = false;
+            for obligation in std::mem::take(&mut obligations) {
+                let obligation = infcx.resolve_vars_if_possible(obligation);
+                match ProvePredicate::fully_perform_into(
+                    obligation.param_env.and(ProvePredicate::new(obligation.predicate)),
+                    infcx,
+                    &mut region_constraints,
+                    span,
+                ) {
+                    Ok(((), _, new, certainty)) => {
+                        obligations.extend(new);
+                        progress = true;
+                        if let Certainty::Ambiguous = certainty {
+                            obligations.push(obligation);
                         }
                     }
-                    if !progress {
-                        infcx.dcx().span_bug(
-                            span,
-                            format!("ambiguity processing {obligations:?} from {self:?}"),
-                        );
-                    }
+                    Err(_) => obligations.push(obligation),
                 }
-                Ok(output)
-            },
-            "fully_perform",
-            span,
-        )?;
-        output.error_info = error_info;
-        if let Some(constraints) = output.constraints {
-            region_constraints
-                .member_constraints
-                .extend(constraints.member_constraints.iter().cloned());
-            region_constraints.outlives.extend(constraints.outlives.iter().cloned());
+            }
+            if !progress {
+                infcx
+                    .dcx()
+                    .span_bug(span, format!("ambiguity processing {obligations:?} from {self:?}"));
+            }
         }
-        output.constraints = if region_constraints.is_empty() {
-            None
-        } else {
-            Some(infcx.tcx.arena.alloc(region_constraints))
-        };
-        Ok(output)
+
+        Ok(TypeOpOutput {
+            output,
+            constraints: if region_constraints.is_empty() {
+                None
+            } else {
+                Some(infcx.tcx.arena.alloc(region_constraints))
+            },
+            error_info,
+        })
     }
 }

tests/ui/inference/issue-80409.no-compat.stderr

@@ -1,4 +1,4 @@
-error: internal compiler error: error performing operation: fully_perform
+error: internal compiler error: error performing ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing }, value: ImpliedOutlivesBounds { ty: &'?2 mut StateContext<'?3, usize> } }
   --> $DIR/issue-80409.rs:49:30
    |
 LL |     builder.state().on_entry(|_| {});